Of the 21 proteinogenic amino acids we use, 9 essential ones can’t be created by our bodies, and therefore need to be attained through food. Many foods are complete proteins, though, meaning they contain sufficient proportions of all essential amino acids. This is why thinking of “protein” rather than “amino acid” as a dietary element is usually sufficient.

In an area of the world where people have traditionally reserved meat eating mostly for special occasions and feast-days, we have found evidence that the ancient state provisioned the pyramid city with enough cattle, sheep, and goat to feed thousands of people prime cuts of meat for more than a generation—even if they ate it every day.